Device for emitting electromagnetic radiation at a predetermined wavelength

ABSTRACT

A device for emitting radiation it a predetermined wavelength is disclosed. The device has a cavity comprising a first bulk region and a second bulk region of opposite conductivity type wherein a barrier is provided for spatially separating the charge carriers of the first and the second region substantially at the antinode of the standing wave pattern of said cavity. The recombination of the charge carriers at the barrier create radiation, the emission wavelength of the radiation being determined by the cavity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to the field of devices emittingelectromagnetic radiation. More in particular, a semiconductor devicethat emits radiation at a predetermined wavelength is disclosed. Amethod of producing such device and applications of such device are alsodisclosed.

2. Description of the Related Art

Semiconductor devices that can emit non-coherent or coherentelectromagnetic radiation are known in the art. A number of publicationson semiconductor based electromagnetic radiation emitters deals withLight Emitting Diodes (LEDs) or Microcavity LEDs or Microcavity Lasersor Vertical Cavity Surface Emitting Lasers. Examples of suchpublications are:

H. De Neve, J. Blondelle, R. Baets, P. Demecster, P. Van Daele, G.Borghs, IEEE Photon. Technol. Lett. 7 287 (1995);

E. F. Schubert, N. E. J. Hunt, R. J. Malik, M. Micovic, D. L. Miller,“Temperature and Modulation Characteristics of Resonant-CavityLight-Emitting Diodes”, Journal of Lightwave Technology, 14 (7),1721-1729 (1996);

T. Yamauchi and Y. Arakawa, Enhanced and inhibited spontaneous emissionin GaAs/AlGaAs vertical microcavity lasers with two kinds of quantumwells. Appl. Phys. Lett. 58 (21), 2339 (1991);

T. J. de Lyon, J. M. Woodall, D. T. McInturff, R. J. S. Bates, J. A.Kash, P. D. Kirchner, and F. Cardone, “Doping concentration dependenceof radiance and optical modulation bandwidth in carbon-doped Ga_(0.1)In_(0.49)P/GaAs light-emitting diodes grown by gas source molecular beamepitaxy” Appl. Phys. Lett. 60 (3), 353-355 (1992);

D. G. Deppe, J. C. Campbell, R. Kuchibhotla, T. J. Rogers, B. G.Streetman, “Optically-coupled mirror-quantum well InGaAs—GaAs lightemitting diode”, Electron. Lett. 26 (20), 1665 (1990);

M. Ettenberg, M. G. Harvey, D. R. Patterson, “Linear, High-Speed,High-Power Strained Quantum-Well LED's”, IEEE Photon. Technol. Lett. 4(1), 27 (1992);

U.S. Pat. No. 5,089,860 Deppe, et al. Feb. 18, 1992, “Quantum welldevice with control of spontaneous photon emission, and method ofmanufacturing same”;

EP-0550963 of Cho, et al “An Improved Light Emitting Diode”.

The presence of a combination of critical parameters in the fabricationof Vertical Cavity Surface Emitting Lasers (VCSELs) makes such laserssuffer from nonuniformity effects over an epitaxially-grown wafer.Examples of parts of said VCSELs with critical parameter values are thetwo distributed Bragg Reflectors (DBRs), the cavity thickness and thethickness of the quantum well (i.e. the active region). This problem sofar has limited array-production of operational VCSELs to 8*8 arrays. An8*8 VCSEL array was disclosed in the publication “Fabrication ofHigh-Packaging Density Vertical Cavity Surface-Emitting Laser ArraysUsing Selective Oxidation” IEEE Phot. Techn. Lett. 8, 596 (1996), byHuffaker et al. Furthermore, the high current density needed forefficient operation of lasers (due to the threshold current needed forachieving inversion) limits the simultaneous operation of many laserelements in array applications. In addition, though VCSELs allowhigh-speed small-signal modulation, VCSELs cannot be used efficientlyfor high-speed large-signal modulation due to the presence of athreshold current.

The development of Microcavity light-emitting diodes (μ cavity LEDs) hascreated efficient and spectrally-narrow semiconductor light sourcesother than lasers in general and VCSELs in particular. In contrast tolasers, μ cavity LEDs do not suffer from any threshold behavior.State-of-the-art Microcavity LEDs have only one DBR, a wavelength cavityand one or more quantum wells that need to be matched in thickness,making design and production less critical. The absence of a thresholdin Microcavity LEDs results in far lower current densities beingrequired for array applications. The increased electrical to opticalpower efficiency of state-of-the-art μ cavity LEDs as compared toconventional LEDs improves the applicability of these μ cavity LEDs inapplications such as optical interconnection systems (in particular asarrays of electromagnetic radiation-emitters) and display applicationsand systems that are critical on the power budget. State-of-the-art μcavity LEDs use one or more quantum wells in the center of the cavity(see FIG. 1) that all have to be identical and matched to the cavitywavelength. Electrons and holes flow from opposite sides into thequantum wells and recombine. Switch-on and switch-off of the μ cavityLEDs are in essence radiative recombination time limited or RC timeconstant limited depending on which one is shorter. The use of severalquantum wells has proven to be essential to reduce saturation in onequantum well, but moves the carrier localization away from thelocalization at the anti-node of the standing-wave pattern in thecavity. The use of several quantum wells also slows the response and theswitch-on and switch-off of the μ cavity LEDs.

However, for array production of μ cavity LEDs, as for instance foroptical interconnects, non-uniformities in the growth of these μ cavityLED and the signal modulation speed remain critical issues. In thedesign of μ Cavity LEDs one makes use of a quantum well to ensurecarrier recombination at the center of the cavity standing-wave pattern(see H. De Neve, J. Blondelle, R. Baets, P. Demeester, P. Van Daele, andG. Borghs in IEEE Photon. Technol. Lett. 7, 287 (1995)). In the designof other state-of-the-art μ cavity LEDs such as disclosed by J.Blondelle, H. De Neve, P. Demeester, P. Van Daele, G. Borghs and R.Baets in El. Lett. 31, 1286 (1995) three quantum wells were used toboost efficiency. In said publication, the efficiency of a μ cavity LEDis boosted by preventing saturation, at the cost of moving part of theactive layer away from the localization at the anti-node of thestanding-wave pattern in the cavity making the efficiency enhancementless pronounced. Thickness variations of the quantum well across asample move the emission wavelength in the different area's of thesample away from the cavity wavelength which reduces the externalefficiency. Furthermore, this device requires the thickness of thequantum well to be exactly matched to the wavelength of the cavity.

Ultra-high speed modulation in semiconductor-based electromagneticradiation emitting devices in prior art publications so far wasdisclosed only for VCSELs or inefficient LEDs. T. J. de Lyon, J. M.Woodall, D. T. McInturff, R. J. S. Bates, J. A. Kash, P. D. Kirchner,and F. Cardone, in “Doping concentration dependence of radiance andoptical modulation bandwidth in carbon-doped Ga_(0.1) In_(0.49)P/GaAslight-emitting diodes grown by gas source molecular beam epitaxy” Appl.Phys. Lett. 60 (3), 353-355 (1992) disclose a method of makinghigh-speed LEDs by highly doping the active region of the LED, whichleads to fast non-radiative recombination and hence a high-speedresponse of the LED. The resulting gain in speed however is more thancompensated by a reduction in quantum efficiency which is incompatiblewith its use in arrays.

EP-0473983 discloses a light emitting device, the device concept ofwhich uses cavity quantum electrodynamics. This device concept is basedin the presence of a quantum well layer adjacent to a barrier layer. Thedevice concept of EP-0473983 suffers a.o. from the problems of:

limited power performance;

slow switch-off time; and

emission wavelength shift during operation.

AIM OF THE INVENTION

It is an aim of the present invention to provide a semiconductor-baseddevice emitting electromagnetic radiation, which has a high quantumefficiency, and wherein the precise thickness of the layers composingthe device are not critical. The fact that the thicknesses of the layerscomposing the device are not critical will allow higher yield in growingthe structures and higher yield across a wafer. The absence of carriertrapping phenomena in the device according to the invention allows fastcharge separation and thus leads to ultra-high-speed, large-signalmodulation previously only observed in VCSELs or inefficient LEDs.

The present invention removes the critical thickness of the quantum well(or more quantum wells) of prior art light-emitting devices by replacingit with a bulk layer or a bulk structure, so as to ensure homogenousefficiency over a larger array of devices over a wafer. To ensure noloss in external efficiency, carrier localization at the anti-node ofthe standing-wave pattern in the cavity is obtained by the addition of abarrier layer with non-critical thickness. This leads to anelectromagnetic radiation emitting device with very high externalefficiency and with a minimal variation in device characteristics whenan array of devices is formed on one semiconductor wafer.

SUMMARY OF THE INVENTION

A device for emitting electromagnetic radiation at a predeterminedwavelength is disclosed, said device having a cavity comprising a firstbulk region of one conductivity type and a second bulk region ofopposite conductivity type and wherein a barrier is provided forspatially separating the charge carriers of said first and said secondbulk region, said barrier being near the antinode of the standing wavepattern of said cavity, the recombination of the charge carriers of thedifferent conductivity types at/across the barrier creating saidradiation. The emission wavelength of said radiation is affected orinfluenced by said cavity. Said first bulk region is adjacent to andabuts said barrier. Said second bulk region is adjacent to and abutssaid barrier. With bulk region, it is meant a region of sufficientthickness for having the quantisation effects on the charge carriersbeing negligibly and much smaller than the thermal energy (kT) of thecharge carriers. Thus, the quantisation effects of a bulk region are notmeasurable in the emission of the radiation and these effects have noimpact compared to the line width of the emitted wavelength. Thus, suchbulk region, e.g. is not a quantum well. Said barrier can be a thirdregion in said cavity providing a barrier for transport of said chargecarriers in-between said first and said second region, the chargecarriers of one conductivity type thereby being trapped at one side ofsaid barrier in either one of said first or second regions, the chargecarriers of the other conductivity type being injected from the otherside of said barrier, the recombination of the charge carriers of thedifferent conductivity type creating said radiation.

The device can further comprise a mirror being provided on the surfaceof one of said first or said second region; and a mirror orsemi-transparent mirror being provided on the surface of another of saidfirst or said second region. An array of such devices can be madewherein said devices are provided on one substrate. Said first and saidsecond regions can each consist in essentially a first material with afirst bandgap, the third region consisting essentially in a thirdmaterial with a third bandgap.

In an alternative embodiment of the present invention, said first andsaid second regions consist in essentially a first material andessentially a second material respectively with a first and a secondbandgap respectively. The first region and the second region in bothembodiments can also comprise layers of a fourth or fifth or furthermaterials.

The cavity can be a single wavelength cavity, a so-called λ-cavity. Thecavity can also be a so-called nλ-cavity. These terms λ-cavity andnλ-cavity are well-known in the art, such a cavity being also well-knownin the art.

Further is disclosed a method of producing a device for emittingelectromagnetic radiation at a predetermined wavelength, comprising thesteps of: depositing a first layer including a first material with afirst bandgap and having a refractive index n₁ and with charge carriersof a first conductivity type on a substrate; depositing a third layer ofa third material with a third bandgap on said first layer, said thirdbandgap being larger than said first bandgap; and depositing a secondlayer of substantially the same thickness as said first layer on saidthird layer, said second layer being provided with charge carriers of asecond conductivity type, the total thickness of said first and saidsecond regions having a value of about said predetermined wavelengthdivided by n₁; while maintaining during said deposition steps at leastone surface of said first layer and one surface of said second layeressentially parallel. The method can further comprise the step ofdepositing a mirror layer on said substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the band diagram of a state-of-the-art μ cavity LED devicefor achieving high external efficiency.

FIG. 2 shows a schematic cross-sectional view of an electromagneticradiation-emitting device according to an embodiment of the presentinvention.

FIG. 3 shows part of the band diagram of the electromagneticradiation-emitting device according to an embodiment of the presentinvention.

FIG. 4 shows the principle of operation of the electromagneticradiation-emitting device according to an embodiment of the presentinvention.

FIG. 5 shows the spectral optical output for several drive currents forthe electromagnetic radiation-emitting device according to an embodimentof the present invention.

FIG. 6 shows the angular distribution of the emitted electromagneticradiation of the electromagnetic radiation-emitting device according toan embodiment of the present invention.

FIG. 7 shows the optical power output versus electrical drive current ofthe electromagnetic radiation-emitting device according to an embodimentof the present invention.

FIG. 8 shows the optical response versus time for the electromagneticradiation-emitting device according to an embodiment of the presentinvention.

FIG. 9 compares the transient response of the electromagneticradiation-emitting device according to the present invention andstate-of-the art LEDs. The devices of the present invention havenominally identical layers, nominally identical quantum efficiency, buthave different ITO contacts. The characteristics of a conventional GaAsquantum well LED without microcavity and of a conventionaldouble-heterostructure LED without quantum well and without microcavity.

FIG. 10 shows a comparison of the power to electromagnetic radiationconversion efficiency of the electromagnetic radiation-emitting deviceof the present invention with state-of-the-art semiconductor basedelectromagnetic radiation emitting devices.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is described in detail in the sequel in relationto the appended drawings. Several embodiments, including a preferredembodiment are disclosed. It is apparent, however, that the personskilled in the art can imagine several other equivalent embodiments orother ways of practicing the present invention, the spirit and scopethereof being limited only by the terms of the appended claims.

A preferred embodiment of the present invention, involves a device foremitting electromagnetic radiation at a predetermined wavelength. Thedevice has a first and a second region of substantially the samethickness each consisting essentially in a first material with a firstbandgap and having a refractive index n₁, the first region has chargecarriers of a first conductivity, and the second region has chargecarriers of a second conductivity type. The total thickness of the firstand the second region has a value of about the predetermined wavelengthdivided by n₁. At least one surface of the first region and one surfaceof the second region are essentially parallel; the device further has athird region consisting essentially of a third material with a thirdbandgap in-between the first and the second region, the third bandgapbeing larger than the first bandgap. The total precise thickness of thefirst and the second regions and the thickness of the third region aredetermined according to a calculation optimizing these differentthicknesses depending on the choice of the materials and radiationefficiency constraints according to the principles of the invention.

The device of the preferred embodiment is provided on a substrate, thesubstrate consisting essentially of the first material, the first andsecond and third regions being in an epitaxial relationship one withanother. According to the preferred embodiment, the first material andthe third material are selected from the group of III-V semiconductingmaterials, the radiation being electromagnetic radiation, the specificwavelength of the electromagnetic radiation being dependent on thespecific III-V material. In the case that the first material is GaAs,the emission wavelength will be in the range of 820 to 900 in and about855 nm. In the case that the first material is AlGaAs, the emissionwavelength will be in the range of 700 to 865 nm. In the case that thefirst material is InGaAs, the emission wavelength will be in the rangeof 855 to 900 nm. In the case that the first material is InAs, theinitial wavelength will be in the range of 3500 nm. The charge carriersof the first conductivity type are electrons or holes, and the chargecarriers of a second conductivity type are holes or electronsrespectively.

FIG. 2 shows a preferred embodiment of the present invention. A GaAselectromagnetic radiation-emitting device is provided. Thiselectromagnetic radiation-emitting device emits electromagneticradiations at a predetermined wavelength λ. λ is preferably in the rangeof 820 to 900 nm, the bulk emission wavelength of n-doped GaAs being 855nm. This device comprises a conductive bottom mirror (4). The conductivebottom mirror (4) can be fabricated to reflect or have a predeterminedemission wavelength in the range of about 820 to about 900 nm.Alternatively, this broad wavelength range mirror (4) can be aDistributed Bragg Reflector (DBR) or a metallic mirror. Thesemiconductor electromagnetic radiation-emitting device furthercomprises a wavelength (λ)-cavity (1) being made of GaAs, with a thinAlAs layer (2) at the antinode of the standing-wave pattern in thewavelength-cavity (1) (in this case the center of the cavity). Thethickness of the AlAs layer (2) can be about 6 to 8 nm; in general thelayer in the center of the cavity should be sufficiently thin to allowfor tunnelling or for thermo-ionic emission of charge carriers(electrons or holes) through the layer. The charge carriers in the GaAslayers (7, 8) of the λ-cavity (1) on either side of the AlAs layer (2)are to be of the opposite type. For example, the GaAs can be doped withSi-atoms, forming n-type charge carriers (electrons) or with Be-atoms,forming p-type charge carriers (holes). In an alternate embodiment,AlGaAs can be used as a top layer on top of each GaAs layer to reducethe absorption of the cavity, which in turn results in more efficientemission. In such case, an AlGaAs layer and a GaAs layer constitutetogether the first region and the second region. The wavelength cavityis to have a thickness in this first embodiment of the invention ofabout 250 nm (λ divided by the refractive index of GaAs). Theelectromagnetic radiation-emitting device further comprises a conductivetop mirror (3). The conductive top mirror (3) can be theGaAs/transparent contact interface or again a DBR. It can also be aAlO_(x)/GaAs mirror structure. Ohmic contacts (5, 6) can further beprovided to either mirror (3, 4).

FIG. 3 depicts a part of an exemplary band diagram for an exemplaryembodiment of the present inventor. The band diagram reflects the bands(7 a, 8 a) for the first and second regions (7, 8) and the band (2 a)corresponding to the barrier layer (2). The band diagram also depictswider bands 9 which correspond to layers reducing the absorption of thecavity, as explained above.

In a second embodiment, the semiconductor electromagneticradiation-emitting device is deposited on a GaAs substrate. Possibly,the structure can be grown by molecular beam epitaxy. A typical growthcomprises the following layers.

(i) A bottom mirror, preferably a Distributed Bragg Reflector (DBR)reflecting the desired emission wavelength λ. This DBR is a stack of λ/4GaAs and AlAs layers (or AlGaAs/AlAs layers) in this embodiment, but canbe any material consisting of λ/4 layers of two materials with adifferent index of refraction;

(ii) An AlGaAs λ-cavity with a thin AlAs layer in the center of thecavity (i.e. at the maximum of the standing-wave pattern for thewavelength of the cavity).

(iii) A top mirror consisting of the AlGaAs/air interface. This mirrorcould also be a thin metallic film, or a DBR or an AlO_(x)/GaAsstructure.

(iv) A transparent Indium Tin Oxide (ITO) contact is sputtered on thesample using photolithographically-defined mesas. This transparentIndium Tin Oxide (ITO) film is used as an ohmic contact. In principle,any ohmic contact ring could also be used provided it covers asufficiently small area of the sample to allow for electromagneticradiation emission when using ITO mesas. Mesas can be defined withoutadditional lithography using wet chemical etching. The currentstate-of-the-art mesa etch stops 10-40 nm above the active layer tominimize surface recombination effects.

In an example of the invention, as detailed below, the samples are grownby molecular beam epitaxy on n+ (Si)-doped GaAs substrates and comprisea n+ (3eE18 cm−3) GaAs buffer layer (approximately 600 nm), aDistributed Bragg Reflector (DBR) consisting of 10 periods (58.2 nmGaAs/71.1 nm AlAs) n+ (3E18 cm−3), i.e. λ/4 layers for the desiredwavelength of operation, followed by a wavelength cavity. The wavelengthcavity consists of a 62 nm n+ (3E18 cm−3) doped AlGaAs optimalizationlight-output A10.3Ga0.7As cladding/bottom contact layer followed by a 25nm (3E18 cm−3) GaAs bottom contact layer, a 20 nm GaAs (1E17 cm−3)spacer layer, a 5 nm undoped GaAs spacer layer, a 8 nm undoped AlAsbarrier layer, a 5 nm undoped GaAs spacer layer, a 20 nm p-GaAs(Be-doped) (1E 17 cm−3) spacer layer, a 25 nm p+-GaAs (Be-doped) (3E18cm−3) cladding/contact layer, a 64 nm p+doped (3E18 cm−3) Al0.3Ga0.7Ascladding/contact layer, and finally a 10 nm heavily p-doped (1E20 cm−3)GaAs top contact layer.

The top mirror is formed by the GaAs/air or after processing theGaAs/ITO interface. ITO stands for Indium Tin Oxide and is used as acontact material.

In summary the epitaxial structure is composed of:

10 nm GaAs:Be 1e20 (top) 64 nm Al.3Ga.7As:Be 3e18 25 nm GaAs:Be 3e18 20nm GaAs:Be 1e17 5 nm GaAs 8 nm AlAs 5 nm GaAs 20 nm GaAs:Si 1e17 25 nmGaAs:Si 3e18 62 nm Al.3Ga.7As:Si 3e18 71.1 nm AlAs:Si 3e18 58.2 nmGaAs:Si 3e18 71.1 nm AlAs:Si 3e18 ---| *9 58.2 nm GaAs:Si 3e18 ---| 500nm GaAs:Si 3e18 (bottom) Substrate GaAs 2″ n-doped

The 71.1 nm AlAs down to 58.2 GaAs constitutes a Distributed BraggReflector. *9 indicates a repetition of the layers.

The doping sequence can be inverted: p-doped substrate, p-doped bottomcontact, and n-doped top contact layers.

The above layer structure was designed for electromagnetic radiationemission at 855 nm.

The principle of operation of the electromagnetic radiation emittingdevice of the present invention is as follows.

(i) The proposed device structure provides vertical localization of theelectromagnetic radiation emission by inclusion of a barrier layer,preferably a single barrier layer. Electrons and holes accumulate oneither side of the barrier (10, 11) (see FIG. 4). The electrons form a2-Dimensional Electron Gas (2DEG) in the accumulation layer. The mainsource of electromagnetic radiation is assumed to be a recombination(13) that takes place between these electrons and the boththermoionically and by tunnelling (12) injected holes. The use of a 2DEGand the high accumulation in a single 2DEG versus the use of severalquantum wells in the state-of-the-art optimizes the microcavity effectsas will be apparent from the optical experiments.

(ii) In the electron accumulation layer (10), the quantization energy inthe 2DEG is very small, leading to an emission wavelength that shows anegligible dependence on geometry. This creates a substantially constantemission wavelength (in essence the bulk emission wavelength) over awafer which is not the case when using a quantum-well layer according tothe state of the art.

As a result, the electromagnetic radiation emitting device of thepresent invention achieves very homogeneous efficiency over anepitaxially-grown wafer due to constant bulk emission combined withweakly dependent mirror/cavity change. The efficiency of conventionalstate-of-the-art electromagnetic radiation emitting devices depends onthe thickness of the active layer and the cavity. In addition, theelectromagnetic radiation emitting device of the present invention has alow capacitance: the single-barrier allows fast charge separation andleads to ultra-high-speed large signal modulation. Gbit/s modulation hasbeen demonstrated.

The Optical characteristics of the electromagnetic radiation-emittingdevice according to the present invention are as follows: under forwardbias, the device emits electromagnetic radiation at the cavitywavelength (855 nm in the example). Because of the low reflectivity ofthe top mirror (by using the air/ITO interface as a top mirror), theangular distribution of the emitted electromagnetic radiation is stillLambertian and spectral narrowing is also not observed. The opticalspectra for several drive currents (0.3 mA, 1 mA and 10 mA) are shown inFIG. 5. Line widths of the emitted electromagnetic radiation of theelectromagnetic radiation emitting device according to the presentinvention are 25 nm and saturation effects are not observed. Line widthbroadening is also very small. The angular distribution of the emittedelectromagnetic radiation is shown in FIG. 6. The emission is purelyLambertian, identical to a conventional LED. For comparison, the angulardistribution of a reference standard LED is measured and plotted in FIG.6 as well as the calculated Lambertian line shape.

The optical power output of the device of the example was measured usinga calibrated optical power meter at a given distance from theelectromagnetic radiation emitting device according to the presentinvention thereby collecting a calibrated fraction of the total power.The total power is plotted versus DC drive current in FIG. 7. From theoptical power follows the external quantum efficiency$\eta = \frac{P_{opt}}{I_{drive}*E_{photon}}$

The external quantum efficiency amounts to 8% for the electromagneticradiation-emitting device of the present invention in good agreementwith the simulated value of 9% for the given device layer structure.

The speed of the device according to the example of the presentinvention is measured by large signal modulation. Electrical pulses from0 V to 3 V forward bias with 60 ps rise time and 120 ps fall time wereapplied and the optical response was measured. Optical collection usedeither a 1 GHz Hamamatsu optical detector in combination with a 2.5 GHzTektronix digitizing oscilloscope or a Hamamatsu streakscope (25 pstiming resolution). The optical response is shown in FIG. 8. The 10-90%rise and fall times amount to 800 ps, from which a 3dB frequency of 0.6GHz is derived. The rise and fall times are four times shorter thanconventional LEDs which have been tested for comparison (see FIG. 9).

Tunnelling LEDs without λ cavity were made for comparison and show riseand fall times of only 180 ps, corresponding to a 3 dB frequency of 2.2Ghz. The present limitation of the devices of the present invention isthought to be due to the large contact resistance of the ITO-GaAscontact, which was not used for the tunnelling LEDs without the λcavity.

FIG. 10 illustrates a comparison of the power to electromagneticradiation conversion efficiency of devices made in accordance with thepresent invention with state-of-the-art semiconductor basedelectromagnetic radiation emitting devices.

The electromagnetic radiation emitting device of the present inventioncan be used for short-distance telecommunication applications or generaldisplay applications.

Another application can be in a system for providing an opticalinterconnect between two chips. The system is a basic building structurefor parallel optical interconnects between chips. Image fibers, wellknow from medical imaging, and used, a mong others places in endoscopes,transport an image from one place to another with a one to onecorrelation between light input and light output image. Arrays ofelectromagnetic radiation emitting devices can be spaced very densely,in arrays on a pitch of 50 micron or even less. Such an array ofelectromagnetic radiation emitting devices forms together with an imagefiber a basic structure for a parallel optical interconnect. By abuttingthe image fiber even without lenses or tapers to the array ofelectromagnetic radiation emitting devices being integrated on forinstance a CMOS chip, a parallel optical interconnect is formed. Thesignals being generated in this chip are transmitted through the arrayof electromagnetic radiation emitting devices to a second chip. Glue oradhesive forms a means to fabricate a solid construction. The personskilled in the art of chip-packaging knows which glue can be used, andhow alignment can be obtained. The electromagnetic radiation emittingdevices of the present invention are bonded on the CMOS chip and theelectrical signals generated in the CMOS chip trigger theelectromagnetic radiation emission of one or a plurality of theelectromagnetic radiation emitting devices of the array. The emittedelectromagnetic radiation is transmitted through the image fiber and isdetected in an optical thyristor or a CMOS based detector being bondedor integrated in the second chip.

What is claimed is:
 1. A device for emitting electromagnetic radiationat a predetermined wavelength, said device comprising: a cavity having afirst bulk region of one conductivity type and a second bulk region ofanother conductivity type, wherein said first bulk region and saidsecond bulk region are of substantially the same thickness and compriseessentially a first material with a first bandgap and having arefractive index n₁, said first bulk region having charge carriers of afirst conductivity type, said second bulk region having charge carriersof a second conductivity type, the total thickness of said first andsaid second bulk region having a value of about said predeterminedwavelength divided by n₁, at least one surface of said first region andone surface of said second region being essentially parallel, andwherein a barrier is provided for spatially separating the chargecarriers of said first bulk region and said second bulk region, saidbarrier being substantially at an antinode of a standing wave pattern ofsaid cavity, the recombination of the charge carriers at the barriercreating said radiation, said first region being adjacent to saidbarrier and said second region being adjacent to said barrier; and athird region consisting essentially of a third material with a thirdbandgap in-between said first and said second region, said third bandgapbeing larger than said first bandgap.
 2. The device as recited in claim1, wherein the emission wavelength of said radiation is affected by saidcavity.
 3. The device as recited in claim 1, wherein said barrier is athird region in said cavity providing a barrier for transport of saidcharge carriers between said first region and said second region, thecharge carriers of either one of said conductivity types thereby beingtrapped at either one side of said barrier in either one of said firstor second regions, the charge carriers of the other conductivity typebeing injected from the other side of said barrier, the recombination ofthe charge carriers of the different conductivity type creating saidradiation.
 4. The device as recited in claim 1, wherein said barrier issufficiently thin to allow for tunnelling or for thermo-ionic emissionof the charge carriers through or respectively over said barrier.
 5. Anarray of devices as recited in claim 1, each of said devices emittingradiation at substantially the same wavelength.
 6. A device for emittingelectromagnetic radiation at a predetermined wavelength, said devicecomprising: a cavity comprising a first bulk region of one, conductivitytype and a second bulk region of another conductivity type, wherein saidfirst bulk region and said second bulk region are substantially the samethickness, the first bulk region comprising essentially in a firstmaterial with a first bandgap and having a refractive index n₁, thesecond bulk region comprising essentially in a second material with asecond bandgap and having a refractive index n₂, said first bulk regionhaving charge carriers of a first conductivity type, said second bulkregion having charge carriers of a second conductivity type, the totalthickness (d) of the thickness of said first bulk region (d₁) and thethickness of said second bulk region (d₂) having a value d equal toabout d₁+d₂ and being essentially determined according to the relationn₁ d₁+n₂ d₂=λ, λ being said predetermined wavelength, and wherein abarrier is provided for spatially separating the charge carriers of saidfirst bulk region and said second bulk region, said barrier beingsubstantially and an anitnode of a standing wave pattern of said cavity,the recombination of charge carriers at the barrier creating saidradiation, said first region being adjacent to said barrier and saidsecond region being adjacent to said barrier; and a third regionconsisting essentially of a third material with a third bandgapinbetween said first and said second region, said third bandgap beinglarger than said first bandgap.
 7. The device as recited in claim 6,further comprising a mirror being provided on the surface of one of saidfirst or said second region; and a semi-transparent mirror beingprovided on the surface of another of said first or said second region.8. The device as recited in claim 7, being provided on a substrate. 9.The device as recited in claim 8, wherein said substrate, said first,said second and said third regions are in an epitaxial relationship. 10.The device as recited in claim 8, wherein said first material and saidthird material are selected from the group of III-V semiconductingmaterials, said radiation being light.
 11. The device as recited inclaim 10, wherein said charge carriers of a first conductivity type areelectrons and said charge carriers of a second conductivity type areholes.
 12. The array of devices as recited in claim 11, wherein saiddevices are provided on one substrate, said substrate consistingessentially of said first material.
 13. The device as recited in claim10, wherein said charge carriers of a first conductivity type are holesand said charge carriers of a second conductivity type are electrons.14. The device as recited in claim 13, wherein said first material isGaAs and said third material is AlAs, and wherein said mirror is aDistributed Bragg Reflector selectively reflecting said predeterminedwavelength.
 15. The device as recited in claim 6, further comprising amirror being provided on the surface of one of said first or said secondregion; and a semi-transparent mirror being provided on the surface ofanother of said first or said second region.
 16. The device as recitedin claim 15, being provided on a substrate.
 17. The device as recited inclaim 16, wherein said substrate, said first, said second and said thirdregions are in an epitaxial relationship.
 18. The device as recited inclaim 16, wherein said first material and said third material areselected from the group of III-V semiconducting materials, saidradiation being light.
 19. The device as recited in claim 18, whereinsaid charge carriers of a first conductivity type are electrons and saidcharge carriers of a second conductivity type are holes.
 20. The deviceas recited in claim 18, wherein said charge carriers of a firstconductivity type are holes and said charge carriers of a secondconductivity type are electrons.
 21. The device as recited in claim 20,wherein said first material is GaAs and said third material is AlAs, andwherein said mirror is a Distributed Bragg Reflector selectivelyreflecting said predetermined wavelength.